Remove juampynr from MAINTAINERS.txt

Thank you for opening and help through out the years!

Thanks Juampy!

Committed to 11.x, 11.2.x, 10.6.x, and 10.5.x. I also updated the core project node and the core maintainer channel.

xjm → closed merge request !12649

Automatically closed - issue fixed for 2 weeks with no activity.